In general, AS (Access Server) devices support multilink connections from subscribers of a telephone network to a packet switched network like the Internet. A multilink represents connections in which a subscriber uses several physical links within one logical connection to the Internet. When forming multilink connections, the major problem is that typically the physical connections between the subscriber and the AS device are terminated in different hardware entities at the AS device.
However, because of packetization of user data to a single logical Internet connection, the several physical connections used for the single logical connection actually have to be terminated at one hardware entity at the AS device. Thus, forming one logical connection consisting of different physical connections can be handled only by using tunneling protocols. For example, in case of multilink connection containing two physical connections, the first physical connection is tunneled from the hardware entity of the AS device at which it is terminated to the hardware entity of the AS device at which the second physical connection is terminated. This tunneling may use either internal transmission paths of the AS device or the Internet itself.
However, the above-described tunneling method raises several problems. The tunneling of user data from one hardware entity of the AS device to another increases the load of these elements. Moreover, using the Internet for tunneling the user data, unmanageable problems may occur because of unpredictable behavior of the Internet.